The present invention relates generally to hinge fasteners for conveyor belts, and more particularly to the rivets used to secure the individual connector members of such fasteners to the conveyor belts.
As disclosed in the aforesaid U.S. Pat. No. 3,742,557, the entire contents of which are hereby incorporated herein by reference, a hinge fastener of the type here under consideration includes rigid, perferably U-shaped, paired connector members each adapted to be riveted to a respective end of the belt. Each connector member includes an upper and a lower plate connected to one another by a plurality of relatively narrower, laterally spaced, U-shaped portions, with these portions of any given connector member when riveted to the belt being arranged in an interfitting relation to the U-shaped portions of the paired connecter member. A hinge pin, usually a steel cable having a plastic coating or sheath thereon to reduce friction, is received in the housing defined by the aligned interiors of the U-shaped portions of the connector members to enable the same to pivot freely about the hinge pin relative to one another.
As will be clear to those skilled in the art, a rivet to be used in securing such a connector member to a belt should preferably be blunt-ended in order to facilitate the upsetting operation required to form the second rivet head after the rivet has been driven through the belt. Since a blunt rivet per se cannot be readily driven into the belt material, however, and, if it were so driven, would tend severely to damage the structure of the belt, i.e. either the elastomeric body material or the reinforcing cords incorporated therein or both, the use of sharp-pointed rivets has been suggested in the prior art. Representative of these are U.S. Pat. No. 3,176,358, British Pat. No. 860,147, and German Pat. No. 845,775. This approach, however, entails either losing the advantages of having the rivet blunt-ended or requiring special expedients, such as the formation of notches or weakened portions in the rivet body just behind the sharp end thereof, to enable the pointed end portion to be broken off preparatory to the performance of the upsetting operation.
In an attempt to combine the advantages of the two types of rivets while avoiding the disadvantages thereof, it was at first proposed, as is pointed out in the aforesaid U.S. Pat. No. 3,742,557, to affix to the unheaded end of a blunt rivet a sharp-pointed mandrel having an outer diameter greater than that of the rivet body. The underlying thought was that such a mandrel could easily penetrate the belt body and form a hole therein through which it would be followed by the attached rivet. Upon removal of the mandrel after full passage of the rivet through the belt, the blunt end of the rivet would then be accessible for the required upsetting operation. Nevertheless, this approach, too, had some drawbacks. With the outer diameter of the mandrel greater than that of the rivet body, the hole formed in the conveyor belt is oversized with respect to the rivet. As a result, the rivet is loosely received in the conveyor belt. The disadvantage of this is that a rivet installed in such an oversized hole may skew therein and may fail to properly fasten the associated connector member to the belt. Furthermore, the mandrel, being press-fitted or similarly secured to the rivet, is not self-extracting or self-releasing and remains affixed to the rivet until removed therefrom by a separate, subsequent operation. Thus, a considerable amount of time and labor has to be expended in removing the mandrel from the rivet, which results in ensuing higher product costs.